1. Field of the Invention
The present invention relates to a base station for a mobile communication network, and more particularly, to a down converter using a C/N ratio correcting circuit of a base station for a mobile communication network that is capable of correcting a degradation of a down converter.
2. Description of the Background Art
Generally, a down converter is a frequency conversion apparatus for converting a radio frequency (RF) signal to an intermediate frequency (IF).
FIG. 1 is a schematic block diagram of the down converter of a base station for a mobile communication network in accordance with a conventional art.
As shown in the drawing, a conventional down converter 12 includes an amplifier 1 for amplifying an RF signal received from an antenna, a band pass filter 2 for passing only a specific band RF signal, attenuators 3 and 4 for attenuating electric power of an input signal and outputting it, a frequency down mixer 5 for converting an RF signal to an IF signal, amplifiers 6 and 8 for amplifying the input signal and outputting it; an SAW (Surface Acoustic Wave) filter 7 for extracting only a specific signal, a splitter 9 for receiving an inputted IF signal and splitting it to two units, an IF processor 10 for processing the IF signal split by the splitter 9, and an RSSI (Received Signal Strength Indicator) voltage detect circuit 11 for receiving the IF signal and generating a voltage level in proportion to the strength of the signal.
The operation of the down converter of the base station for a mobile communication network of the conventional art constructed as described will now be explained.
First, the RF signal received from a part is collected by the antenna and applied to the amplifier 1.
The amplifier 1 amplifies the received RF signal and transmits it to the band pass filter 2.
The band pass filter 2 passes only a specific band of the received RF signal and transmits it to the attenuators 3 and 4.
The attenuators 3 and 4 lower down electric power of the RF signal received from the band pass filter 2 to a predetermined level and transmit it to the frequency down mixer 5.
The frequency down mixer 5 converts the received RF signal to an IF signal and transmits the IF signal to the amplifier 6.
The amplifier 6 amplifies the IF signal received from the frequency down mixer 5 to compensate the conversion loss and transmits the amplified IF signal to the SAW filter 7.
The SAW filter 7 extracts a specific signal from the received IF signal and transmits the specific signal to the amplifier 8.
The IF signal amplified by the amplifier 8 is transmitted to the splitter 9.
The splitter 9 splits the receives IF signal to the IF signal processor 10 and the RSSI voltage detect circuit 11. The IF signal split to the IF signal processor is applied to a digital processor.
The RSSI voltage detect circuit 11 receives the split IF signal and generates a voltage level in proportion to the strength of the IF signal.
As to the down converter 12 of the base station for a mobile communication network, substantially, the RSSI voltage detect circuit 11 has no other function than the function of generating a voltage level, and even the voltage level generated by the RSSI voltage detect circuit 11 is not employed for any other units. Thus, the down converter is constructed with omission of the RSSI voltage detect circuit 11.
FIG. 2 is a diagram showing a concept of a carrier/noise (C/N) ratio.
Generally, the carrier/noise (C/N) ratio is a factor indicating a receiving capability of the base station for a mobile communication network. Elements on the down convert path, such as the amplifiers 1, 6 and 8, the filters 2 and 7, the attenuators 3 and 4, or the frequency down mixer 5, affects the C/N ratio. In addition, the degradation of the receiving capability of the base station for a mobile communication network such as the deterioration or the reduction of the C/N ratio attributes to the loss of the down convert path.
Conventionally, in the base station for a mobile communication network, a solution to the problems was merely to replace the down converter itself or an internal element.